The invention relates to a breech mechanism for particular use in hand firearms and having a breech piston which pushes a cartridge into a cartridge chamber and which has at least two radially projecting bolt elements. The breech mechanism also has a breech casing, which comprises a breech piston bore, a longitudinal groove for each bolt element and an annulus in which the breech piston bore and each of the longitudinal grooves open and which is provided with a rear engageable supporting surface. Further, a breech sleeve of the mechanism has a groove that is in alignment with the longitudinal groove of the breech piston bore in an open feed position for each bolt element, and is rotatably arranged in the annulus between the open feed position and a locked end position.
Such a breech mechanism is shown, for example, in DE-C 515 972. The breech sleeve totally fills the annulus and the cavity of the breech sleeve is filled by the pushed-in breech piston head and its bolt elements. In so doing, the rear face of the breech sleeve overlaps the longitudinally extending grooves of the breech piston bore. Thus, there is no free space and the breech piston bore is sealed better.
U.S. Pat. No. 3,738,223 shows a breech mechanism with a conical breech piston head on which is mounted a deformable element, which carries an extractor for the cartridge case and which is deformed when the cartridge chamber is locked. The increased contact of the deformed regions against the conical surfaces of the annulus and the breech piston head, and against the groove region of the cartridge case improves the breech-side seal of the cartridge chamber.